1. Field of the Invention
This invention relates to an electronic timepiece and, especially, to the timepiece system with an improved voltage characteristic. A threshold voltage based regulator circuit adapts the voltage of the battery to the best operation voltage of the integrated circuit comprised in the timepiece system.
2. Description of the Prior Art
Heretofore, when an operational voltage of an electronic timepiece is predetermined, the reference voltage of its display section is a voltage which has the operational lower limit voltage of the display elements and the battery voltage. For example, the operational voltage of a timepiece circuit is predetermined at 1.5 volts of a battery cell and that of a liquid crystal display circuit is preset at DC-DC converted up to 3.0 volts, and a level shift circuit is used for driving a display system.
However, several improvements need to be considered in the above-mentioned systems with the view of reducing power consumption.
Firstly, it is not essential that a timepiece circuit should be directly operated by a battery cell voltage. If the voltage of the timepiece circuit is lowered to a lower limit voltage determined by theoretical and practical considerations, a supply voltage may also be able to be reduced to the limit voltage. Furthermore, the impedance of the timepiece circuit is invariable and the power consumption may be reduced in proportion to the inverse of the supply voltage.
Secondly, of course, the operational starting voltage of an integrated circuit depends on its characteristics, but, for example, the threshold value of each transistor in an integrated circuit such as C-MOS FET (Complementary Metal Oxide Silicon Field Effect Transistors) deviates depending upon the process condition of manufacture of the integrated circuit, whereby the current consumption changes in proportion to the square of the number of the difference between a supply voltage and operational starting voltage. Therefore, wasteful power consumption is large in a practical timepiece circuit design when taking into account its oscillation gain margin concerning the distribution of deviations and fluctuations of the battery voltage. Thus, if the battery cell and the timepiece circuit are coupled with each other through a circuit means having a buffer function about the voltage difference, the power consumption may be reduced substantially.
Thirdly, it is not significant that each of the circuit blocks exists individually. It is significant that a signal can be delivered to another circuit and the structure is designed so that the circuits effect a function similar to the function of a conventional circuit notwithstanding the fact that some circuit blocks are operating at a reduced voltage. For example, a circuit having a function of transacting energy such as driving of display elements or a pulse motor may be combined with a reference signal circuit. For this purpose, it is required that provision be made for a level shift circuit to raise the voltage which is lower than that of the battery voltage and for delivering the raised voltage to the other circuit.